The deoxynucleoside, 2-chloro-2'-deoxyadenosine, is known (D. A. Carson, D. Bruce Wasson, and Ernest Beutler, Proc. Soc. Acad. Sci. USA, Vol. 81, pp 2232-2236, 1984) for its antileukemic and immunosuppressive activity both in mammals and in Phase 1 clinical trial in patients.